Elevated concentrations of plasma low density lipoprotein cholesterol (LDL-C), a major risk factor for coronary heart disease, cluster significantly in families. This clustering has been observed in cross-sectional studies in both black and white families, but longitudinal data on the familial clustering of LDL-C are virtually nonexistent. The proposed study will provide new and important information about changes in the familial LDL-C correlations in black and white families from the period of shared household environments to that of separate households, using families from the Princeton Lipid Research Clinics (LRC) Prevalence (1973-75) and Family Studies (1975-76). The proposed study will also provide important information on changes in individual LDL-C levels over the same 25 year period. The former student participants were six to 18 years of age and are now 32 to 45 years of age; their parents were (largely) 26 to 55 years of age and are now 51 to 80 years of age. Plasma LDL-C concentrations in children and adults have been shown to associate with the apolipoprotein (apo) E genotype, with obesity, and with such elective behaviors as diet, cigarette smoking, and physical activity. In the LRC Study, measurements were made of LDL-C, body habitus, elective behaviors, and the family history of cardiovascular disease (CVD). The proposed study will obtain repeat measures of these factors, plus determine the apo E isoforms. Changes in individual LDL-C levels and in familial associations can then be assessed in association with apo E isoforms, body composition, elective behaviors, and family history of CVD. Family members share ranges of body weight, patterns of fat distribution, dietary and smoking habits, and physical activity levels. The extent to which the familial clustering of LDL-C levels is determined by apo E isoforms interacting with the similar levels of obesity, and with the similar behaviors, is not currently known. The investigators state that data from this study will provide new insights into mechanisms for the clustering of LDL-C levels. They further state that the factors influencing long term changes in LDL-C levels will be clarified and an understanding of environmental and genetic influences gained. They conclude that this information can be used to improve prediction of future CHD risk and to formulate interventions.